1. Field of the Invention
The present invention relates to centrifugal compressors, and more particularly, to a rotor mechanism of a centrifugal compressor for blocking leakage of lubricants and recycling of lubricants.
2. Description of the Prior Art
With continual advancement in compressor technology, requirements for rotational speeds and performance of compressors also increase. As shown in FIG. 1, U.S. Pat. No. 4,938,664 has disclosed an oil reclaim system for use in a centrifugal compressor, wherein a high-pressure refrigerant is used to drive and guide the lubricant to go from an inlet 102 to an oil sump 101 along the lower border of the casing. The refrigerant is rotationally compressed by vanes 100. A jet pump 106 pumps the lubricant to go from an opening 105 to the oil sump 101 via a low-pressure pipe 104. Subjected to the pumping of the jet pump 106, a high-pressure refrigerant gas goes from an opening 108 to the oil sump 101 via a high-pressure pipe 107 so as to block the lubricant from accumulating in the lower region after the refrigerant is introduced.
Although U.S. Pat. No. 4,938,664 provides a design for recycling lubricant, it does not teach effective means for blocking contamination of refrigerant loop caused by leakage of lubricants. This is particularly true in the case where the refrigerant loop is the high pressure end and a hydrodynamic bearing is used to support a rotary shaft, because a longer period of time is required to establish supporting oil pressure during actuation. The reason for such a requirement is that it is extremely easy for the lubricant to leak into the refrigerant loop to contaminate the purity of the refrigerant if a pressure difference is not established. Moreover, hydrodynamic bearings are known for poor efficiency, low rigidity, and long time for establishing oil pressure establishing time as mentioned previously. Surfaces of the hydrodynamic bearings are extremely soft, such that they are extremely likely to be damaged when the compressor comes to a sudden halt. Also, if the lubricant liquids fail to meet the high purity requirement for refrigerants, they may be mixed with the lubricant gases when the lubricant gases are being separated.
Referring to FIG. 2, U.S. Pat. No. 4,997,340 has disclosed a sealing device for use in a buffer region of a centrifugal compressor, wherein the sealing device is used for sealing a transmission region and a motor power region, to reduce drop in efficiency and to prevent the refrigerant from leaking into the motor power region from the transmission region. The sealing device comprises a labyrinth seal 113 installed between a buffer region 112 and a transmission region 109. The labyrinth seal 113 contacts the region where an impeller 110 is situated via a pore. Because the pressure of air current compression and refrigerant gas in the region is slightly higher than that in the transmission region 109, leakage of the lubricant into the buffer region 112 (connected to the motor power region) is stopped and the lubricant are guided back to the oil sump 111 after the pressure of the high-pressure refrigerant gas has reached the labyrinth seal 113.
Although U.S. Pat. No. 4,997,340 is better than the prior art by teaching the labyrinth seal 113, the cochlear pressure of the centrifugal compressor is still low when the centrifugal compressor is actuated and the lubricant for lubricating a bearing may leak into the refrigerant loop along the high-speed shaft or through the labyrinth seal 113. The leakage must therefore be blocked to avoid loss of lubricants, particularly since the hydrodynamic bearings are known for poor efficiency, low rigidity, and long time for establishing oil pressure when actuated, as well as easy damages to the extremely soft surfaces thereof when the compressor comes to a halt suddenly. After actuation, the high-pressure refrigerant compressed by the impeller 110 may also leak into a lower pressure area along gaps, resulting in a loss of the refrigerant and a decrease in the compressor efficiency. Thus, to increase the compressor efficiency, it is necessary to block the leakage.
The two aforesaid patents can provide effective recycling of lubricant for centrifugal compressors, but there are doubts on the efficiency of separation of refrigerants and lubricant sealing. In particular, it would be a major defect if the leakage of lubricants into the region where the impellor is positioned cannot be blocked. At the same time, by simply implementing the labyrinth seal cannot ensure insulation, because longer time is required for establishing a pressure and the maintenance of the centrifugal compressor is poor. Moreover, due to the axial force arisen from a dorsal pressure difference, the use of a single impellor is also likely to cause leakage.